The value of primers in aircraft painting and finishing is usually underestimated and misunderstood as it is invisible after application of the topcoat finish. Nevertheless, a primer serves as the foundation of finish. The role of primer is bonding to the surface, inhibiting metal corrosion, and providing an anchor point for coats of the finish.
The primer pigments should either be anodic to surface of the metal or passivate the metal surface if moisture is present. The binder and the finish coats should be compatible with each other. Primers for surfaces that are nonmetallic, don’t require passivating or sacrificial pigments.
Following are some of the chief primer types used for aircraft painting and finishing.
Primers for Aircraft Painting and Finishing
1. Wash Primers
Wash primers are coating of phosphoric acid in a solution of alcohol, vinyl butyral resin, and other ingredients. These primers give water-thin coatings, have very low amounts of solids, and have no filling qualities. The functions of these primers are passivating the surface, providing corrosion resistance temporarily, and offering an adhesive base for next coatings, like an epoxy or urethane primer.
Wash primers have remarkable corrosion protection qualities and don’t need sanding. The recoat timeframe for some of them is very short that should be taken into account while painting larger airplanes. Follow the manufacturers’ instructions to get satisfactory results.
2. Gray Enamel Undercoat
This is a nonsanding, single component primer compatible with various topcoats. Gray enamel undercoat has a high corrosion resistance, dries quickly without any shrinkage, and fills minor imperfections.
3. Red Iron Oxide
An alkyd resin-based primer coating, red oxide primer was developed to be used over steel and iron in mild environmental conditions. You can apply it over rust which is free of grease, oil, and loose particles. This primer type’s use is limited in aviation industry.
A thermosetting, synthetic resin, epoxy produces hard, tough, chemical-resistant adhesives and coatings. Epoxy uses a catalyst for activating the product chemically, but it’s not identified as hazardous as it doesn’t contain any isocyanates. This primer type can be employed as a nonsanding sealer/primer over bare metal. It’s softer compared to urethane and has a good chip resistance. Epoxy is recommended to be used over steel tube frame airplanes before installing fabric covering.
5. Zinc Chromate
A corrosion resistant pigment, zinc chromate can be added in primers made of various types of resins, like alkyd, polyurethane, and epoxy. Zinc chromate of older type can be distinguished by its bright yellow hue as compared to the current brand primers that usually have a light green color. Zinc chromate reacts with metal surfaces because of moisture present in the air, forming a passive layer which prevents corrosion. At one time, zinc chromate was the standard primer for painting of airplanes. However, it has now been replaced due to environmental concerns and the emergence of new formula primers.
These are the key types of primers used in aircraft painting and finishing. If you are looking for airplane painting services, Boca Aircraft Maintenance can provide you quality aircraft painting and finishing services. Being one of the leading aircraft painting companies in Florida, we specialize in aircraft exterior painting.